1. Field of the Invention
This invention relates to an improved absorption refrigeration method and apparatus. The invention relates more particularly to a method and apparatus for increasing the temperature of a fluid which supplies operating energy to an absorption refrigeration apparatus.
2. Description of the Prior Art
An absorption refrigeration apparatus, with which the present invention is concerned, is known in the art and generally includes an evaporator means in heat transfer relationship with a fluid to be chilled, a condenser means in heat transfer relationship with a means for discharging to the atmosphere thermal energy removed from the chilled fluid, and an absorber/generator means. Operating energy for the apparatus is supplied to the generator principally in the form of thermal energy. In one type of absorption refrigeration apparatus, thermal energy is supplied to the generator by a heated fluid which is conveyed in heat exchange relationship, through the generator. When a relatively low cost fluid heating medium is available for use in transferring heat to the generator, the cost of operation in terms of energy input are advantageous.
The absorption type of refrigeration system operates efficiently when a fluid providing thermal energy to the generator is supplied within a range of supply temperatures. In general, the particular range of supply temperatures (T.sub.1 -T.sub.2) is dependent upon the refrigerant medium utilized with the absorption refrigeration apparatus. An absorption refrigeration apparatus employing lithium bromide as a refrigerant operates efficiently when the heated fluid supplied to the generator is provided at a temperature in the range of 190.degree. F.-210.degree. F. while the temperature range for an ammonia refrigerant lies between 250.degree. F.-300.degree. F. As indicated, the absorption refrigeration apparatus provides energy cost advantages when thermal energy is available within the indicated temperature range. At times however thermal energy is available but at temperatures which, while relatively high, are still below that range of temperatures at which the absorption refrigeration apparatus efficiently operate.
Various techniques have been used for supplementing energy available with fluids at a temperature less then the efficient operating temperature of the absorption refrigeration apparatus and raising the temperature of the fluid to the desired range (T.sub.1 -T.sub.2). These techniques have provided for the use of electrical energized heating elements or the use of a gas fired means for raising the temperature of the supply fluid. However, the absorption refrigeration apparatus has a coefficient of performance of less than one and energy supplied with these techniques for increasing the temperature of the supply fluid can more efficiently be used to directly operate the refrigeration equipment therefor. In one technique, this drawback is partially compensated by recovery of some useful work by the reexpansion of air after it passes through a heat exchanger. Nonetheless air is a poor heat transfer medium and unless a heat exchanger is relatively large and a substantial volume of air flows through it, inadequate energy will be delivered to the absorption refrigeration apparatus to satisfy increasing load requirements.
It is also desirable to limit the temperature decrease of the supply fluid as it is circulated between the generator heat exchanger and a reservoir containing the heated fluid. However, when the temperature of this heated fluid is raised by an auxiliary external energy means to cause the apparatus to operate at maximum efficiency, the output stream of the generator heat exchanger is substantially higher in temperature than the reservoir temperature of the fluid and the auxiliary temperature enhancing source is then required to supply a substantial proportion of the energy for operating the absorption refrigeration apparatus.